Scientific Method —

Researchers open door to electronics made from single layers of atoms

Film of graphene and boron nitride acts like a circuit board one atom thick

Artist's impression of a nanoscale electronic device made of graphene (carbon atoms, in gray) and boron nitride (BN, purple and blue). The graphene is conducting, the BN is insulating, so by laying down patterns, single-layer electronic devices can be fabricated.

A new frontier in nanoscale and flexible electronics has emerged in the last decade, based on thin materials consisting of just a few layers of atoms. However, unlike conventional semiconductor devices, precise control over electronic properties may involve placing individual atoms at precise locations in the material. While this certainly can be done with modern technology (atomic force microscopy and similar tools utilize this tech), significant barriers still exist to mass-producing thin electronic devices.

Researchers at Cornell University have discovered a potentially valuable method which they label patterned regrowth. In a Nature report, Mark P. Levendorf and his coauthors described this process for creating a film of graphene (a single layer of carbon atoms) combined with boron nitride (BN) in the same single-atom-thick lattice. Since graphene is a conductor and BN is an insulator, the researchers were able to control the electronic properties of the film precisely. This research could allow the fabrication of integrated circuits in sheets whose thickness is just one or a few atoms deep. Additionally, future work along these lines could achieve transparent electronics.

Modern electronics are built on integrated circuits: arrays of semiconductor devices such as transistors connected by conducting material (often copper). These pieces, often assembled as circuit boards, are cheap, easy to manufacture, and therefore ubiquitous. If nanoscale electronics are to be useful, they must be at least be easy to produce: it doesn't matter how cool the gadget is if it can only be made one at a time in a special university research lab.

Enter the patterned regrowth technique. The researchers deposited a layer of graphene on copper foil, then removed portions of the graphene. Next, they overlaid a second layer, consisting of BN or more graphene, which could be doped—containing molecules such as hydrogen (H2) or ammonia (NH3)—to alter the electronic properties of the graphene. (Doping is commonly used in semiconductors to produce the precise electronic configuration needed for devices.) Since the new layer filled in the regions removed from the first layer, the authors obtained sharp boundaries between the conducting graphene and the insulating BN or the doped graphene. In electronics terms, this is known as a junction.

Since graphene conducts and boron nitride does not, the resulting pattern acted analogously to a printed circuit, with conducting "wires" and regions where current cannot flow. Though the chemistry is markedly different, the major difference was that the entire assembly was a single atom in thickness. In the published paper, in fact, the copper substrate was clearly visible through the single layer of atoms.

Graphene-based electronics have been shown to be highly flexible in previous trials; having true single-atomic-layer electronics that can be produced easily is a major move toward practical flexible devices. The researchers noted that they could add single-layer semiconductors such as molybdenum disulfide (MoS2); as semiconductors are the basis for all modern electronics, introducing them into thin flexible devices would allow even more capabilities for future applications. Finally, while the film of atoms in this technique was overlaid on an opaque surface, the authors pointed out that its inherent transparency could be exploited, leading the way to truly transparent electronics.